With the constant development of communications technologies, a user can access a core network of an operator through any of the following access methods: Global System for Mobile communications/Enhanced Data rates for GSM Evolution Radio Access Network (GERAN), Universal Mobile Telecommunication System Terrestrial Radio Access Network (UTRAN), and evolved UTRAN (eUTRAN).
When a user moves between networks, to maintain continuity of user services, seamless handover between access technologies such as GERAN, UTRAN, and eUTRAN is required.
In the prior art, users who adopt a Subscriber Identity Module (SIM) or run SIM applications on a Universal Integrated Circuit Card (UICC) are called SIM users. When a SIM user communicates in a UTRAN or GERAN network and moves to a border between an eUTRAN and the UTRAN or GERAN, if the signal strength of the eUTRAN is stronger than that of other access networks, or if a service requires, the source network may select the eUTRAN as the target network for network handover and switch the user to the eUTRAN temporarily through a normal handover process. In this case, the SIM user can temporarily use the resources of the core network and then execute Authentication and Key Agreement (AKA). The SIM, however, does not support AKA. Therefore, if the SIM user is identified during this process, the connection of the SIM user to the eUTRAN is terminated.
During the implementation of the present invention, the inventor discovers the following disadvantages in the prior art: The existing technology implements the function of forbidding a SIM user to access an eUTRAN. After the SIM user temporarily switches to the eUTRAN, the eUTRAN rejects the access of the SIM user according to the AKA result. At this time, the SIM user is disconnected from the originally available network, which leads to service interruption.